传统的os 比如ucos 这种维护了一个头为单指针的双向链表，这样导致链表插入到尾部的速度很慢，得不偿失，所以raw os 采用了头为双指针的双向链表，插入速度更快。-Traditional OS such as UCOS the maintain a head for a single needle two-way linked list. As a result, the linked list insertion to the tail of the speed is very slow, not worth the candle, so raw OS using the head is a pointer to a double two-way linked list, insert faster.